allow writing snapshot on top of existing files

CONTRIBUTING.md

@@ -68,6 +68,17 @@ testing. Your contribution needs to meet the following standards:
 - Document all your public functions.
 - Add a descriptive message for each commit. Follow
   [commit message best practices](https://github.com/erlang/otp/wiki/writing-good-commit-messages).
+- A good commit message may look like
+
+  ```
+  A descriptive title of 50 characters or fewer
+
+  A concise description where each line is 72 characters or fewer.
+
+  Signed-Off-By <A full name> <A email>
+  Co-Authored-By: <B full name> <B email>
+  ```
+
 - Document your pull requests. Include the reasoning behind each change, and
   the testing done.
 - Acknowledge Firecracker's [Apache 2.0 license](LICENSE) and certify that no

docs/kernel-policy.md

@@ -61,6 +61,7 @@ on which Firecracker is run:
 ### ARM
 
 * timekeeping - `CONFIG_ARM_AMBA`, `CONFIG_RTC_DRV_PL031`
+* serial console - `CONFIG_SERIAL_OF_PLATFORM`
 
 ### x86_64
 

docs/snapshotting/snapshot-support.md

@@ -154,16 +154,16 @@ The Firecracker snapshotting implementation offers support for snapshot versioni
   Firecracker release `v` might drop the possibility to save snapshots at any
   versions older than `v`.
 
-  For example Firecracker v1.0 adds support for some additional virtio features
-  (e.g. notification suppression). These features lead the guest drivers to
-  behave in a very specific way and as a consequence the Firecracker devices
-  have to respond accordingly. As a result, the snapshots that are created
-  while these features are in use will not be backwards compatible with
+  For example Firecracker v1.0 and v1.1 adds support for some additional virtio
+  features (e.g. notification suppression). These features lead the guest
+  drivers to behave in a very specific way and as a consequence the Firecracker
+  devices have to respond accordingly. As a result, the snapshots that are
+  created while these features are in use will not be backwards compatible with
   previous versions of Firecracker since the devices that come with these older
   versions do not behave in a way that’s compatible with the snapshotted guest
   drivers.
 
-  The list of versions that break snapshot backwards compatibility: `1.0`
+  The list of versions that break snapshot backwards compatibility: `1.0`, `1.1`
 - Loading snapshots from older versions (being able to load a snapshot created
   by any Firecracker version in the `[N, N + o]` interval, in a Firecracker
   version `N+o`).

src/arch/src/aarch64/mod.rs

@@ -30,6 +30,8 @@ pub enum Error {
 
 /// The start of the memory area reserved for MMIO devices.
 pub const MMIO_MEM_START: u64 = layout::MAPPED_IO_START;
+/// The size of the memory area reserved for MMIO devices.
+pub const MMIO_MEM_SIZE: u64 = layout::DRAM_MEM_START - layout::MAPPED_IO_START; //>> 1GB
 
 /// Returns a Vec of the valid memory addresses for aarch64.
 /// See [`layout`](layout) module for a drawing of the specific memory model for this platform.

src/arch/src/lib.rs

@@ -17,7 +17,8 @@ pub mod aarch64;
 #[cfg(target_arch = "aarch64")]
 pub use aarch64::{
     arch_memory_regions, configure_system, get_kernel_start, initrd_load_addr,
-    layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE, layout::IRQ_MAX, regs, Error, MMIO_MEM_START,
+    layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE, layout::IRQ_MAX, regs, Error, MMIO_MEM_SIZE,
+    MMIO_MEM_START,
 };
 
 /// Module for x86_64 related functionality.
@@ -27,7 +28,8 @@ pub mod x86_64;
 #[cfg(target_arch = "x86_64")]
 pub use crate::x86_64::{
     arch_memory_regions, configure_system, get_kernel_start, initrd_load_addr,
-    layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE, layout::IRQ_MAX, Error, MMIO_MEM_START,
+    layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE, layout::IRQ_MAX, Error, MMIO_MEM_SIZE,
+    MMIO_MEM_START,
 };
 
 /// Type for returning public functions outcome.

src/arch/src/x86_64/mod.rs

@@ -42,9 +42,12 @@ pub enum Error {
 // Where BIOS/VGA magic would live on a real PC.
 const EBDA_START: u64 = 0x9fc00;
 const FIRST_ADDR_PAST_32BITS: u64 = 1 << 32;
-const MEM_32BIT_GAP_SIZE: u64 = 768 << 20;
+/// Size of MMIO gap at top of 32-bit address space.
+pub const MEM_32BIT_GAP_SIZE: u64 = 768 << 20;
 /// The start of the memory area reserved for MMIO devices.
 pub const MMIO_MEM_START: u64 = FIRST_ADDR_PAST_32BITS - MEM_32BIT_GAP_SIZE;
+/// The size of the memory area reserved for MMIO devices.
+pub const MMIO_MEM_SIZE: u64 = MEM_32BIT_GAP_SIZE;
 
 /// Returns a Vec of the valid memory addresses.
 /// These should be used to configure the GuestMemoryMmap structure for the platform.

src/devices/src/virtio/balloon/device.rs

@@ -13,7 +13,7 @@ use ::timerfd::{ClockId, SetTimeFlags, TimerFd, TimerState};
 
 use ::logger::{error, IncMetric, METRICS};
 use ::utils::eventfd::EventFd;
-use ::virtio_gen::virtio_blk::*;
+use ::virtio_gen::virtio_blk::VIRTIO_F_VERSION_1;
 use ::vm_memory::{Address, ByteValued, Bytes, GuestAddress, GuestMemoryMmap};
 
 use super::*;

src/devices/src/virtio/block/device.rs

@@ -17,9 +17,13 @@ use std::sync::Arc;
 
 use logger::{error, warn, IncMetric, METRICS};
 use rate_limiter::{BucketUpdate, RateLimiter};
+use serde::{Deserialize, Serialize};
 use utils::eventfd::EventFd;
 use utils::kernel_version::{min_kernel_version_for_io_uring, KernelVersion};
-use virtio_gen::virtio_blk::*;
+use virtio_gen::virtio_blk::{
+    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_RO, VIRTIO_BLK_ID_BYTES, VIRTIO_F_VERSION_1,
+};
+use virtio_gen::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
 use vm_memory::GuestMemoryMmap;
 
 use super::io as block_io;
@@ -31,8 +35,6 @@ use super::{
 };
 use crate::virtio::{IrqTrigger, IrqType};
 use block_io::FileEngine;
-use serde::{Deserialize, Serialize};
-use virtio_gen::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
 
 /// Configuration options for disk caching.
 #[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]

src/devices/src/virtio/block/event_handler.rs

@@ -102,16 +102,17 @@ impl MutEventSubscriber for Block {
 pub mod tests {
     use std::sync::{Arc, Mutex};
 
+    use event_manager::{EventManager, SubscriberOps};
+    use virtio_gen::virtio_blk::{VIRTIO_BLK_S_OK, VIRTIO_BLK_T_OUT};
+    use vm_memory::{Bytes, GuestAddress};
+
     use super::*;
     use crate::virtio::block::device::FileEngineType;
     use crate::virtio::block::test_utils::{
         default_block, set_queue, simulate_async_completion_event,
     };
     use crate::virtio::queue::tests::*;
     use crate::virtio::test_utils::{default_mem, initialize_virtqueue, VirtQueue};
-    use event_manager::{EventManager, SubscriberOps};
-    use virtio_gen::virtio_blk::*;
-    use vm_memory::{Bytes, GuestAddress};
 
     #[test]
     fn test_event_handler() {

src/devices/src/virtio/block/request.rs

@@ -9,7 +9,10 @@ use std::convert::From;
 use std::result;
 
 use logger::{error, IncMetric, METRICS};
-use virtio_gen::virtio_blk::*;
+pub use virtio_gen::virtio_blk::{
+    VIRTIO_BLK_ID_BYTES, VIRTIO_BLK_S_IOERR, VIRTIO_BLK_S_OK, VIRTIO_BLK_S_UNSUPP,
+    VIRTIO_BLK_T_FLUSH, VIRTIO_BLK_T_GET_ID, VIRTIO_BLK_T_IN, VIRTIO_BLK_T_OUT,
+};
 use vm_memory::{ByteValued, Bytes, GuestAddress, GuestMemoryError, GuestMemoryMmap};
 
 use super::super::DescriptorChain;